1. Field of the Invention
The present invention is related to hearing systems, devices and methods. Although specific reference is made to hearing aid systems, embodiments of the present invention can be used in many applications in which a signal is used to stimulate the ear.
People like to hear. Hearing allows people to listen to and understand others. Natural hearing can include spatial cues that allow a user to hear a speaker, even when background noise is present. People also like to communicate with those who are far away, such as with cellular phones.
Hearing devices can be used with communication systems to help the hearing impaired and to help people communicate with others who are far away. Hearing impaired subjects need hearing aids to verbally communicate with those around them. Open canal hearing aids have proven to be successful in the marketplace because of increased comfort and an improved cosmetic appearance. Another reason why open canal hearing aides can be popular is reduced occlusion of the ear canal. Occlusion can result in an unnatural, tunnel-like hearing effect which can be caused by large hearing aids which block the ear canal. In at least some instances, occlusion be noticed by the user when he or she speaks and the occlusion results in an unnatural sound during speech. However, a problem that may occur with open canal hearing aids is feedback. The feedback may result from placement of the microphone in too close proximity with the speaker or the amplified sound being too great. Thus, feedback can limit the degree of sound amplification that a hearing aid can provide. Although feedback can be minimized by placing the microphone outside the ear canal, this placement can result in the device providing an unnatural sound that is devoid of the spatial location information cues present with natural hearing.
In some instances, feedback may be decreased by using non-acoustic means of stimulating the natural hearing transduction pathway, for example stimulating the tympanic membrane, bones of the ossicular chain and/or the cochlea. An output transducer may be placed on the eardrum, the ossicles in the middle ear, or the cochlea to stimulate the hearing pathway. However, surgery may be needed to place a hearing device on the ossicles or cochlea, and such surgery can involve delicate and complex movements to position the implant and can be somewhat invasive, for example with the cutting and drilling of bone, in at least some instances. The cutting and/or drilling of bone can delay healing and recovery time, such that implantation of at least some of the prior devices in the middle ear may not be well suited for at least some patients in at least some instances. At least some of the prior implants located on the ossicles or the cochlea can result in occlusion in at least some instances, and distortion of the sound can be perceptible in at least some instances.
One promising approach has been to place a magnet on the eardrum and drive the magnet with a coil positioned away from the eardrum. The magnet can be electromagnetically driven with a coil to cause motion in the hearing transduction pathway thereby causing neural impulses leading to the sensation of hearing. A permanent magnet may be coupled to the ear drum through the use of a fluid and surface tension, for example as described in U.S. Pat. Nos. 5,259,032 and 6,084,975. Although this approach can result in decrease feedback and shows promise, there is still room for improvement. In at least some instances, a magnet positioned on the ear may be sensitive to external electromagnetic fields that can result in a perceptible noise, for example a humming sound in at least some instances.
Another promising approach has been to optically couple a hearing device, such that noise from electromagnetic interference can be decreased. However, in at least some instances the prior systems that transmit light to a transducer can result in perceptible noise and distortion in the optically transmitted signal, such that the sound quality of such devices can be less than ideal in at least some instances. For example, at least some optical systems may comprise non-linearity that can distort the signal and may result in user-perceptible distortion in at least some instances. Work in relation to embodiments of the present invention also suggests that vibration of a photodetector can result in distortion of the transmitted signal, for example when vibration affects optical coupling from a light source to the photodetector. Also, at least some of the proposed optically coupled devices have been affixed to vibratory structures of the ear, which can result in a user perceptible occlusion due to the mass of the device affixed to the vibratory structure of the ear.
For the above reasons, it would be desirable to provide hearing systems which at least decrease, or even avoid, at least some of the above mentioned limitations of the prior hearing devices. For example, there is a need to provide a comfortable hearing device which provides hearing with natural qualities, for example with spatial information cues, and which allow the user to hear with less occlusion, distortion and feedback than prior devices.
2. Description of the Background Art
Patents and publications that may be relevant to the present application include: U.S. Pat. Nos. 3,585,416; 3,764,748; 3,882,285; 5,142,186; 5,554,096; 5,624,376; 5,795,287; 5,800,336; 5,825,122; 5,857,958; 5,859,916; 5,888,187; 5,897,486; 5,913,815; 5,949,895; 6,005,955; 6,068,590; 6,093,144; 6,139,488; 6,174,278; 6,190,305; 6,208,445; 6,217,508; 6,222,302; 6,241,767; 6,422,991; 6,475,134; 6,519,376; 6,620,110; 6,626,822; 6,676,592; 6,728,024; 6,735,318; 6,900,926; 6,920,340; 7,072,475; 7,095,981; 7,239,069; 7,289,639; D512,979; 2002/0086715; 2003/0142841; 2004/0234092; 2005/0020873; 2006/0107744; 2006/0233398; 2006/075175; 2007/0083078; 2007/0191673; 2008/0021518; 2008/0107292; commonly owned U.S. Pat. No. 5,259,032; U.S. Pat. No. 5,276,910; U.S. Pat. No. 5,425,104; U.S. Pat. No. 5,804,109; U.S. Pat. No. 6,084,975; U.S. Pat. No. 6,554,761; U.S. Pat. No. 6,629,922; U.S. Publication Nos. 2006/0023908; 2006/0189841; 2006/0251278; and 2007/0100197. Non-U.S. patents and publications that may be relevant include EP1845919 PCT Publication Nos. WO 03/063542; WO 2006/075175; U.S. Publication Nos. Journal publications that may be relevant include: Ayatollahi et al., “Design and Modeling of Micromachines Condenser MEMS Loudspeaker using Permanent Magnet Neodymium-Iron-Boron (Nd—Fe—B)”, ISCE, Kuala Lampur, 2006; Birch et al, “Microengineered Systems for the Hearing Impaired”, IEE, London, 1996; Cheng et al., “A silicon microspeaker for hearing instruments”, J. Micromech. Microeng., 14(2004) 859-866; Yi et al., “Piezoelectric microspeaker with compressive nitride diaphragm”, IEEE, 2006, and Zhigang Wang et al., “Preliminary Assessment of Remote Photoelectric Excitation of an Actuator for a Hearing Implant”, IEEE Engineering in Medicine and Biology 27th Annual Conference, Shanghai, China, Sep. 1-4, 2005. Other publications of interest include: Gennum GA3280 Preliminary Data Sheet, “Voyager TDTM. Open Platform DSP System for Ultra Low Power Audio Processing” and National Semiconductor LM4673 Data Sheet, “LM4673 Filterless, 2.65 W, Mono, Class D audio Power Amplifier”; Puria, S. et al., Middle ear morphometry from cadaveric temporal bone micro CT imaging, Invited Talk. MEMRO 2006, Zurich; Puria, S. et al, A gear in the middle ear ARO 2007, Baltimore, Md.; O'Connor, K. and Puria, S. “Middle ear cavity and ear canal pressure-driven stapes velocity responses in human cadaveric temporal bones” J. Acoust. Soc. Am. 120(3) 1517-1528.